Measuring instrument for röntgen rays.



R. FU'RSTENAU. MEASURING INSTRUMENT FOR RUNTGEN RAYS. APPLIFIATION FILED l AN.28 I914? 1,229,740. Patented June 12, 1917.

ROBERT FURSTENAU, OF BIRLIN, GERMANY.

MEASURING INSTRUMENT FOR R6NTGEN RAYS.

Specification of Letters Patent.

Patented June 12, 1917.

Application filed January 28, 1914. Serial No. 814,980.

To all whom it may concern:

Be it known that I. Romnrr l i'uis'rnxio, a resident of Berlin. Germany, a subject of the King of Prussia, and whose post-oflico address is 146 Kurfiirstenstrasse. Berlin, Kingdom of Prussia, German Empiredmve invented new and useful Improvements in or Relating to Measuring Instruments for ltiintgen Rays. of which the following is a specification.

Crystalline selenium has the property of 'arying its electric resistance when subjected to the action of Riintgen rays. It is, however, very much less sensitive to Rontgen rays than to the rays-of light so that relatively small resistance variations occur on applyingrays of the intensity which is usual in practlc'e.

Now this invention has for its object to provide a useful measuring instrument for Rontgen rays whereby all the inconveniences hitherto arising out of the use of a cell of selenium are avoided. The novel arrangement consists in the arrangement of the selenium cell in a. branch of a \Vheatstone bridge. The arrangement and the strength of the resistances are so calculated that when the selenium cell is not exposed to any rays a current flows through the galvanometer of the bridge in a direction which is opposite to that of the current flowing through the instrument when the cell is exposed to the rays. By means of this arrangement the great drawbacks which hitherto defeated the practical use of selenium cells for measuring Rontgen rays are entirely dispensed with. No injurious current and heat fluctuations occur in the selenium cell and the pointer of the measuring instrument returns to zero imlnediatel the radiation ceases.

An arrangement of this kind is illust 'ated diagrammaticall by way of example in the accompanying drawing.

1 is the selenium element which is subjected to the rays of the Rontgen tube 7. 2. 3 and J are the resistances in the branches of the bridge. 5 is the battery and 6 the galvanometer.

What I do claim as my invention, and desire to secure by Letters Patent of the United States. is:

A Rontgen ray measuring instrument comprising in combination a VVheatstono bridge having a selenium cell for exposure to the rays in one of its two parallel resistancebranches. and a galvanometer connected across from an intermediate point of one resistance branch to an intermediate point of the other resistance branch; the relative resistance of the branch containing the selenium cell being of a magnitude to cause the current to flow through the galvanoineter in one direction when said cell is exposed to R'c'mtgen rays and in the reverse direction when not exposed, whereby the indicatorof said galvanometer is returned to its normal position immediately after discontinuing the exposure of the selenium cell to the rays.

In testimony whereof I have hereunto set my hand in presence of two subscribing witnesses.

ROBERT FURSTENAU. \Vitnesses VVOLDEMAR HAUPT, HENRY HASPER. 

